Afar triple junction triggered by plume-assisted bi-directional continental break-up

Divergent ridge-ridge-ridge (R-R-R) triple junctions are one of the most remarkable, yet largely enigmatic, features of plate tectonics. The juncture of the Arabian, Nubian, and Somalian plates is a type-example of the early development stage of a triple junction where three active rifts meet at a ‘triple point’ in Central Afar. This structure may result from the impingement of the Afar plume into a non-uniformly stressed continental lithosphere, but this process has never been reproduced by self-consistent plume-lithosphere interaction experiments. Here we use 3D thermo-mechanical numerical models to examine the initiation of plume-induced rift systems under variable far-field stress conditions. Whereas simple linear rift structures are preferred under uni-directional extension, we find that more complex patterns form in response to bi-directional extension, combining one or several R-R-R triple junctions. These triple junctions optimize the geometry of continental break-up by minimizing the amount of dissipative mechanical work required to accommodate multi-directional extension. Our models suggest that Afar-like triple junctions are an end-member mode of plume-induced bi-directional rifting that combines asymmetrical northward pull and symmetrical EW extension at similar rates.

Long-term evolution of the North Anatolian Fault: new constraints from its eastern termination

The deformation and40Ar–39Ar dating of recent volcanism, that remarkably sits across the North Anatolian Fault eastern termination in Turkey, together with previous studies, put strong constraints on the long-term evolution of the fault. We argue that after a first phase of 10 Ma, characterized by a slip rate of about 3 mm/a, and during which most of the trace was established, the slip rate jumped to about 20 mm/a on average over the last 2.5 Ma, without substantial increase of the fault length. The transition correlates with a change in the geometry at the junction with the East Anatolian Fault that makes the extrusion process more efficient.

Complex Shear Wave Velocity Structure Imaged Beneath Africa and Iceland

A model of three-dimensional shear wave velocity variations in the mantle reveals a tilted low velocity anomaly extending from the core-mantle boundary (CMB) region beneath the southeastern Atlantic Ocean into the upper mantle beneath eastern Africa. This anomaly suggests that Cenozoic flood basalt volcanism in the Afar region and active rifting beneath the East African Rift is linked to an extensive thermal anomaly at the CMB more than 45 degrees away. In contrast, a low velocity anomaly beneath Iceland is confined to the upper mantle.